Operation of electronic power controllers, such as a triac light dimmer, can create severe interfering noise in the AM radio band. The interfering noise may enter the radio through any of the mechanisms of capacitive coupling to the antenna, conduction through the AC mains, or magnetic coupling to the antenna. In home use, a major mode is through the AC mains.
Typical antennas for AM radios are external loop or internal loop types, such as ferrite rod loop AM antennas. External loop antennas typically use twisted pair lead-ins connected to a balanced input. Internal ferrite rod loop antennas are typically unbalanced, with one side of the loop at RF ground while the other side is connected to a varactor diode. An unbalanced pickup coil is typically used to drive the detector integrated circuit (IC).
It is an important object of the invention to reduce electrical interference in an AM radio with an improved antenna.